Compared: .257 Roberts and 6.5x55 SE
By Chuck Hawks
This comparison matches two of the classic, all-time great, small-bore cartridges. The .257 Roberts and the 6.5x55 SE are cartridges often chosen by experienced hunters over newer, flashier numbers and both are popular choices for custom-built rifles. They are also cartridges of proven effectiveness whose performance in the field belies their relatively modest performance numbers. Neither kicks very hard, making precise bullet placement easier and we all know that bullet placement is, by far, the most important factor in killing power.
The .257 Roberts
The .257 Roberts is based on a necked-down 7mm Mauser case given a 15-degree shoulder and was originated by Ned Roberts, who named his creation the ".25 Roberts." Remington legitimized the cartridge in 1934, changing the shoulder angle back to 20 degrees (the same as the 7x57) and calling it the ".257 Roberts." From then until the introduction of the .243 Winchester and .244 Remington in 1955, the .257 was the top selling combination varmint/deer cartridge.
The .257 is offered in a number of factory loads with 117-120 grain bullets. Federal Premium offers a factory load using a 120 grain Nosler Partition bullet at a muzzle velocity (MV) of 2,800 fps. Hornady offers a factory load in their Light Magnum line that drives a 117 grain spire point bullet at a MV of 2,940 fps. These are considered to be "+P" loads, because for reasons that no one seems to clearly understand, the .257 was pegged to a SAAMI maximum average pressure (MAP) of 45,000 cup. +P cartridges are loaded to a MAP of 50,000 cup, which is more like it.
Reloaders with modern rifles can safely load to .257 +P pressure and many reloading manuals include +P loads. I had good results in my Ruger No. 1 rifle with the 115 grain Nosler Ballistic Tip bullet, which can be driven to a MV of about 2800 fps by several powders.
The .257 is a bit much for varminting, having considerable muzzle blast for a varmint cartridge, but it is an excellent, low recoil, flat shooting, deer and antelope cartridge. For this purpose, it has a big advantage over the 6mm cartridges, since it makes a bigger hole and can use 115-120 grain bullets that are substantially heavier than the 90-105 grain bullets commonly used for hunting CXP2 game in the 6mm cartridges.
The 6.5x55 SE
This old timer was introduced by the government of Norway and Sweden (at the time they were one country) in 1894 for their then new Mauser and Krag bolt action service rifles. As with most successful military cartridges, the 6.5x55 was quickly adopted by civilian hunters, who found that it was an excellent, general purpose, CXP2 game cartridge that could be "stretched" for use on CXP3 game if required. It quickly became a popular civilian cartridge with both hunters and target shooters around the world and it remains so today.
Despite its age, this is a modern looking, rimless, sharp shouldered cartridge in the current fashion. If it were introduced tomorrow, instead of over 100 years ago, no one would raise an eyebrow. The only departure from current practice is its unusual rim diameter of .4803", rather than the .4730" that later became the norm for standard (non-magnum) cartridges. Back in 1894 there was no "normal" rim diameter for high intensity, smokeless powder cartridges. Fortunately, the 6.5x55's rim diameter is close enough to make no practical difference and the same rifles that are chambered for 7x57, .308 Winchester and .30-06 can also be chambered for 6.5x55.
The original service load used a 160 grain round nose (RN) bullet, but this was later changed to a 140 grain spitzer bullet that has since become the standard for bullet weight for practically all 6.5mm big game hunting cartridges. This is an inherently efficient bullet weight for the 6.5mm (.264") caliber with excellent sectional density (SD) and usually a high ballistic coefficient (BC) as well.
Despite its age, the 6.5x55 remains a very useful and versatile cartridge. Low powered American factory loads such as the Winchester Super-X and Remington Express drive a 140 grain spitzer bullet at a MV of 2550 fps. These mild loads minimize recoil, muzzle blast and kill CXP2 game well. However, the big American manufacturers tend to seriously under load classic European cartridges and higher pressure European factory loads drive the same weight bullet 100 fps to 300 fps faster. Norma, for example, offers a 139 grain Vulkan bullet at a MV of 2854 fps and a 140 grain Nosler Partition at a MV of 2789 fps. For heavy game (the 6.5x55 is a very popular moose cartridge in Scandinavia), Norma loads a 156 grain Vulkan bullet at 2644 fps. These are far more powerful than the anemic American factory loads and American ammo manufacturers would probably consider them to be "+P" loads, although the Europeans do not.
Reloaders with modern rifles can duplicate the European loads. My standard handload drives a 140 grain Sierra GameKing bullet at a MV of approximately 2700 fps, which is entirely adequate for my hunting needs and is a pleasant load to shoot.
The .257 Roberts and the 6.5x55 can drive light for caliber bullets to sufficient velocity for long range varminting, but both burn too much powder to make efficient varmint calibers. Both are better as CXP2 big game calibers and that is how we will compare them here.
To represent the .257 we will use the Federal Premium factory load with its 120 grain Nosler Partition bullet (the heaviest bullet weight normally loaded in the .257) at a MV of 2800 fps. To represent the 6.5x55 we will use the Norma factory load with a 140 grain Nosler Partition bullet (the most popular, but not the heaviest, bullet weight in 6.5mm) at a MV of 2789 fps. Nosler Partition bullets are widely available to reloaders, who can duplicate these ballistics using data straight from the Sixth Edition of the Nosler Reloading Guide. Our comparison loads thus represent both premium factory loads and maximum reloads.
We will compare the .257 Roberts and 6.5x55 SE in sectional density and ballistic coefficient, velocity, energy, trajectory, bullet cross-sectional area, killing power, recoil and the availability of both guns and ammunition. At the end will be a few concluding comments.
Sectional Density and Ballistic Coefficient
Sectional density is defined as a bullet's weight (in pounds) divided by the square of its diameter (in inches). Sectional density is important because, other factors being equal, a long skinny bullet of a given weight penetrates better than a short fat bullet of the same weight.
Ballistic coefficient is a measurement of how well a bullet flies through the air. The higher the BC, the more aerodynamic the bullet and the lower its drag. A higher BC helps a bullet retain more of its initial velocity and energy down range and results in a flatter trajectory. A flatter trajectory makes hitting easier as the range increases. Here are the sectional densities and published ballistic coefficients for the bullets used in our comparison loads.
The BC of the .257 bullet is good, but the BC of the 6.5mm bullet is very good and presumably will help it "hold up" better at long range. The SD's of both bullets are excellent for hunting CXP2 game, where a SD of .225 is considered more than adequate. However, the heavier 6.5mm bullet is a standout in this area, being fully adequate for even the largest CXP3 class game.
Bullet weight has no bearing on cross-sectional (frontal) area, only caliber. The cross-sectional area of a hunting bullet is important because, other factors being equal, a fatter bullet makes a wider wound channel and damages more tissue. This translates to quicker and more humane kills. The actual bullet diameter of the .257 Roberts bullet is .257". The bullet diameter of 6.5mm bullets is .264". Following are the frontal areas of each in square inches.
Obviously, if bullet expansion percentage and penetration are identical, a .264" bullet will always punch a larger diameter hole than a .257" bullet. The difference is not great, but it is there.
Higher velocity means flatter trajectory, given bullets of equal ballistic coefficient. Velocity is also the most important component in the formula used to compute kinetic energy. Here are the velocity figures from the muzzle to 300 yards (beyond the MPBR of both cartridges) in feet-per-second for our selected .257 Roberts and 6.5x55 SE loads, measured in 24" test barrels.
The 6.5x55 bullet starts out slightly slower, but by 100 yards it is already traveling faster due to its superior BC. This bodes well for its down range trajectory.
Kinetic energy is a measure of the ability to do work and it is widely used to compare the power of rifle cartridges. Energy powers bullet penetration and expansion, which are very important elements in killing power. The key factors in computing kinetic energy are bullet mass and the square of bullet velocity. Here are the energy figures for our selected loads in foot-pounds from the muzzle (ME) to 300 yards.
As a rule, you want to retain at least 800 ft. lbs. of energy at bullet impact when hunting CXP2 game. These figures show that both calibers are adequate for the purpose past 300 yards. A load that can deliver a hunting weight bullet carrying over 1200 ft. lbs. is generally considered adequate for the common CXP3 game species, such as Rocky Mountain elk, and while the .257 is marginal due to its relatively light, small diameter bullet, the 6.5x55 qualifies there as well.
Trajectory is important to hunters because the flatter a bullet's trajectory, the easier it is to achieve accurate bullet placement at long and unknown ranges. The primary factors influencing trajectory are bullet velocity and ballistic coefficient.
The best way to compare the trajectory of hunting loads is by their maximum point blank range (MPBR). MPBR is the distance at which the bullet drops 3" below the line of sight and represents the longest range at which shots at big game animals should be taken. Here is the MPBR based trajectory of our comparison loads from 100 to 300 yards.
As you can see from these figures, the 6.5x55 shoots slightly flatter than the .257 and has a five yard advantage in MPBR. This is an inconsequential difference and it is a little hard to imagine a real world hunting situation where an extra 0.7" drop at 300 yards would matter.
Killing power is the most difficult factor to quantify. Optimum Game Weight (OGW) is a system devised by Edward A. Matunas to express the killing power of rifle cartridges in terms of an animal's live weight and the optimum distance at which it can be taken with a given cartridge and load. Thus, it compares the killing power of different cartridges and loads in a way that is relevant in the field.
To reduce the variables, Matunas started with the assumption that bullet design and placement are adequate for the task. We need not go into the formula itself here, suffice to say that while not perfect, the OGW system does seem to have a higher correlation with reality than most other systems for estimating the killing power of big game rifle cartridges. (For more on OGW, see the "Expanded Optimum Game Weight Table" on the Tables, Charts, and Lists Page.) The figures below represent optimum game weight in pounds and distance in yards from the muzzle to 300 yards.
These OGW figures largely confirm what was indicated by the bullets' remaining kinetic energy. Both cartridges and loads are adequate for most species of CXP2 game to or beyond their MPBR and the 6.5x55 is adequate for CXP3 game (roughly 500 pounds) at relatively short range. At least in terms of OGW killing power, the 6.5x55 is considerably the more potent cartridge.
Recoil Energy and Velocity
This is the category that many shooters like to ignore, but it is actually of crucial importance. Bullet placement is, by far, the most important factor in killing power and rifle recoil is the #1 enemy of accurate bullet placement. A hunter who flinches in anticipation of the rifle firing is a great wounder of game. Here are some approximate recoil energy (in foot pounds) and velocity (in fps) figures for our comparison loads when fired in 8 pound rifles.
These numbers show that the 6.5x55 kicks roughly 40% more (in terms of energy) than the .257 Roberts with our comparison loads. This is a significant difference to a recoil sensitive shooter and a noticeable difference to any shooter. Both cartridges/loads are below the 15 ft. lb. level that an "average" hunter might consider comfortable, but the .257 has a big advantage in lower recoil over the 6.5x55.
Recoil velocity accounts for the relative "sharpness" of recoil. While the .257 also has an advantage here, it is proportionally smaller. Neither cartridge would be considered to have a particularly sharp kick by most shooters. For comparison, the common .30-06/180 grain factory load generates recoil energy of about 20.3 ft. lbs. and a 12.8 fps recoil velocity in an 8 pound rifle. Compared to that, these are easy cartridges to shoot!
Guns and Ammunition
The .257 Roberts and 6.5x55 SE have been around for a long time and many rifles have been chambered for them over the years. Today neither is a particularly common caliber in new factory built rifles, but there are more rifle choices in 6.5x55 than .257. Actually, Ruger is the only company I can think of that consistently offers new rifles (their bolt action M77) in .257 Roberts, although there may be others.
If you look, you will usually find three or four brands of new rifles chambered for 6.5x55 on the U.S. market at any given time, although they may have to be special ordered by most dealers. European rifle brands such as CZ, Sako, Sauer, Tikka, Blaser and Merkel are among the likely choices, although Ruger, Winchester and Remington have offered 6.5x55 rifles in recent memory.
There are also, of course, reasonable numbers of surplus Swedish Mauser '96 military rifles on the used market, in both original configuration and sporterized. Most of these are in good, shootable condition and they are relatively inexpensive. Swedish military Mausers were produced in Sweden by Husqvarna and Carl Gustafs and in Germany by Mauser (using only Swedish steel, which the Swedes demanded). They were all very high quality rifles produced to the same exacting standards. Sweden was neutral in both World Wars, so there is no lower quality "wartime" production.
Both the .257 Roberts and the 6.5x55 are popular calibers in fine, custom built rifles. Not surprisingly, they tend to be favored by experienced and knowledgeable shooters of both sexes and some of these folks are able to come up with the scratch to finance bespoke rifles in the caliber of their choice.
In the U.S., all four of the major ammo manufacturers (Federal, Hornady, Remington and Winchester) offer .257 Roberts and 6.5x55 factory loads, as do most of the specialty ammunition providers, such as Stars & Stripes. In Europe, practically all of the ammo companies offer 6.5x55 loads, but not all load for the .257, which is not as popular over there. Norma and Sellier & Bellot are probably the most common brands of imported 6.5x55 ammunition, at least in the Pacific Northwest (where I live). I have no figures to prove it, but I would guess that 6.5x55 rifles and ammo are also more common in Africa and Australia.
As you can see from the foregoing comparison, the 6.5x55 is superior to the .257 Roberts as a big game cartridge in every performance category except recoil. Fortunately, while the 6.5x55 kicks considerably harder than the .257, it is still a moderate recoiling cartridge (below 15 ft. lbs.), much more comfortable to shoot than cartridges in the .270, .308 and .30-06 class. However, for the person looking to keep recoil below 6.5x55 levels, the .257 Roberts is an excellent choice. It kicks about like a .243/6mm cartridge, but kills better.
The .257 Roberts is probably the best of the low recoil, high intensity, CXP2 game cartridges, while the 6.5x55 SE is certainly one of the best moderate recoil cartridges, treading close on the heels of the "all-around" cartridges in performance.
Copyright 2009, 2012 by Chuck Hawks. All rights reserved.